A conventional method of measuring a blood sugar level is exemplified by a method of measuring the blood sampled from a fingertip and so forth by use of a puncture instrument with a disposable test piece on which a dried reagent containing an enzyme is placed (e.g., Patent document 2). There is a method of measuring a glucose concentration not in the blood but in an extracellular fluid (interstitial fluid) by making use of a sensor that is subcutaneously inserted (e.g., Patent document 1).
An electrochemical sensor for detecting a specified component in a sample by making use of enzyme reaction in away that immobilizes the enzyme to a subcutaneously detained sensor unit is employed as the sensor for measuring the glucose concentration in some cases. The electrochemical sensor normally includes a working electrode and a counter electrode, in which the enzyme (e.g., a glucose oxidase) is immobilized to the working electrode. The glucose concentration is measured based on a response current acquired by continuously applying a fixed voltage (e.g., about 0.3V-0.6V) to between the working electrode and the counter electrode.
The blood sugar level (a value of the glucose concentration in the blood) is different from a value of the glucose concentration in the interstitial fluid, and it is therefore necessary to correct the value of the glucose concentration in the interstitial fluid. As a method of correcting the value of the glucose concentration in the interstitial fluid, there is a method of calibrating the value to a value of the glucose concentration in the blood from a response current value acquired due to reaction between the interstitial fluid and the enzyme by use of the value of the glucose concentration in the blood that is obtained from measurement of the sampled blood.
An activity of the enzyme fluctuates depending on a reaction temperature. A subcutaneous temperature largely fluctuates depending on a change in temperature condition ambient to an examinee such as a living environment (e.g., an outdoor air temperature) of the examinee and activities in daily living (such as bathing and taking excises) thereof. In the case of continuously measuring the glucose concentration by the subcutaneous-detention type electrochemical sensor, a measurement result thereof is affected by the fluctuation in subcutaneous temperature as the case may be. Further, in the case of measuring the glucose concentration in the blood by using the sampled blood also, the measurement result is affected by the fluctuation in subcutaneous temperature as the case may be.    Patent document 1: U.S. Pat. No. 6,560,471    Patent document 2: Japanese Examined Patent Application Publication No. 06-58338